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APPENDIX 5.1F
Offsets and Interpollutant Offset Ratio Analysis
APPENDIX 5.1F
Offsets and Interpollutant Offset Ratio Analysis
Under District Rule 2201, A2PP must provide offsets for the portion of the facility emissions
after modification that exceed the SJVAPCD offset thresholds. Because the proposed project
is a modification to an existing stationary source, the calculation of the offset requirements
must account for the emissions from the existing TID Almond power plant facility.
Table 5.1F-1 shows annual proposed potential to emit from the new A2PP units, the annual
potential to emit for the existing units, and the total emissions from the combined facility
after modification, and compares these totals with the offset thresholds to determine the
offsets required for the project.
TABLE 5.1F-1
Offset Requirements for the A2PP
Annual Emissions, tons
NOx SOx VOC PM10
A2PP Project Emissions 70.7 19.4 17.0 32.9
Pre-Existing PTE 26.3 5.7 5.3 8.8
Rule 2201 Offset Threshold 10.0 27.4 10.0 14.6
Emissions Required to be Offset 70.7 0 12.2 27.0
District Rule 2201 allows the APCO to approve interpollutant offsets on a case-by-case basis.
A2PP proposes to use SO2 ERCs as offsets for PM10. The interpolllutant offset ratio analysis
in Attachment 5.1F-1 demonstrates that ratio of 1.0 ton of SO2 for 1 ton of PM10 will provide
equivalent air quality benefits as required under the NSR rules.
The required quarterly calculation of offsets is provided in Table 5.1F-2. This calculation
demonstrates that more than sufficient offsets are being provided to achieve the no net
increase provision of the District NSR rule (Rule 2201 §1.0).
Table 5.1F-3 provides a demonstration that sufficient mitigation is being provided under
CEQA. Table 5.1F-4 provides documentation regarding the location and method of
reduction for each ERC certificate proposed to be used for the project.
EY012009003SAC(A2PP APPENDIX 5.1F_OFFSETS_REV-FINAL.DOC) 5.1F-1
Table 5.1F-2
TID Almond 2 Power Plant
Quarterly Offset Summary (lbs/qtr)
VOC
1st Quarter 2nd Quarter 3rd Quarter 4th Quarter Annual (tpy)
Project VOC Emissions 8,389 8,482 8,576 8,576 17.0
Pre-Existing PTE 2,614 2,614 2,614 2,614 5.2
VOC Offset Threshold (1) 5,000 5,000 5,000 5,000 10.0
VOC Emissions Required to be Offset (2) 6,003 6,096 6,190 6,190 12.2
VOC ERCs Required for District regulations (3) 9,005 9,145 9,284 9,284 18.4
VOC ERCs
C-348-1 10,250 10,250 10,250 10,250 20.5
VOC ERCs Excess (Shortfall) 1,245 1,105 966 966 2.1
NOx
1st Quarter 2nd Quarter 3rd Quarter 4th Quarter Annual (tpy)
Project NOx Emissions 34,885 35,273 35,661 35,661 70.7
Pre-Existing PTE 13,012 13,012 13,012 13,012 26.0
NOx Offset Threshold (1) 5,000 5,000 5,000 5,000 10.0
NOx Emissions Required to be Offset (2) 34,885 35,273 35,661 35,661 70.7
(3)
NOx ERCs Required for District regulations 52,328 52,909 53,491 53,491 106.1
NOx ERCs
S-2991-2 55,800 55,800 55,800 55,800 111.6
Total 55,800 55,800 55,800 55,800 111.6
NOx ERCs Excess (Shortfall) 3,472 2,891 2,309 2,309 5.5
Table 5.1F-2
TID Almond 2 Power Plant
Quarterly Offset Summary (lbs/qtr)
(cont'd)
SOx
1st Quarter 2nd Quarter 3rd Quarter 4th Quarter Annual (tpy)
Project SOx Emissions 9,558 9,664 9,770 9,770 19.4
Pre-Existing PTE 2,865 2,865 2,865 2,865 5.7
SOx Offset Threshold (1) 13,688 13,688 13,688 13,688 27.4
SOx Emissions Required to be Offset (2) 0 0 0 0 0.0
SOx ERCs Required for District Regulations (3) 0 0 0 0 0.0
SOx ERCs
S-2726-5 (Calpine) 55,614 40,150 0 84,936 90.4
Total 55,614 40,150 0 84,936 90.4
SOx ERCs Needed for PM10 19,920 20,190 20,460 20,460 40.5
Allocate 4th Quarter SOx ERCs to 3rd Quarter -- -- 20,460 -20,460 0.0
SOx ERCs Excess (Shortfall) 35,694 19,960 0 44,016 49.8
PM10
1st Quarter 2nd Quarter 3rd Quarter 4th Quarter Annual (tpy)
Project PM10 Emissions 16,200 16,380 16,560 16,560 32.9
Pre-Existing PTE 4,380 4,380 4,380 4,380 8.8
PM10 Offset Threshold (1) 7,300 7,300 7,300 7,300 14.6
(2)
PM10 Emissions Required to be Offset 13,280 13,460 13,640 13,640 27.0
PM10 ERCs Required for District regulations (3) 19,920 20,190 20,460 20,460 40.5
PM10 ERCs
Total 0 0 0 0 0.0
PM10 ERCs Excess (Shortfall) (19,920) (20,190) (20,460) (20,460) (40.5)
PM10 Reductions from SOx ERCs (at 1.0 to 1.0) (4) 19,920 20,190 20,460 20,460 40.5
PM10 Reductions Excess (Shortfall) 0 0 0 0 0.0
Notes:
1. Offset thresholds from SJVAPCD Rule 2201, Table 4.1
2. Offset liability from SJVAPCD Rule 2201, Section 4.7.2
3. Max distance ratio assumed based on SJVAPCD Rule 2201, Table 4.2: 1.5
4. SOx:PM10 ratio evaluation from Attachment 5.1F-1. Use 1.00
Table 5.1F-3
TID Almond 2 Power Plant
CEQA Mitigation Summary
VOC tons per year
Project VOC Emissions 17.0
VOC ERCs Required for CEQA Mitigation 17.0
C-348-1 20.5
VOC ERCs Excess (Shortfall) 3.5
NOx tons per year
Project NOx Emissions 70.7
NOx ERCs Required for CEQA Mitigation 70.7
NOx ERCs
S-2991-2 111.6
Total 111.6
NOx ERCs Excess (Shortfall) 40.9
SOx tons per year
Project SOx Emissions 19.4
SOx ERCs Required for CEQA Mitigation 19.4
SOx ERCs
S-2726-5 (Calpine) 90.4
Total 90.4
SOx ERCs Excess (Shortfall) 71.0
SOx ERCs Used for PM10 32.9
SOx ERCs Excess (Shortfall) 38.1
PM10/PM2.5 tons per year
Project PM10/PM2.5 Emissions 32.9
PM10/PM2.5 ERCs Required for CEQA Mitigation 32.9
PM10 ERCs
Total 0.0
PM10 ERCs Excess (Shortfall) (32.9)
PM10/PM2.5 Reductions from SOx ERCs (at 1.0 to 1.0) (1) 32.9
PM10/PM2.5 Reductions Excess (Shortfall) 0.0
Notes:
1. SOx:PM10 ratio evaluation from Attachment 5.1F-1. Use 1.00
Table 5.1F-4
TID A2PP ERCs
ERC Date of ERCs, lbs
Certificate Reduction Issue date Quarter 1 Quarter 2 Quarter 3 Quarter 4 Annual Previous Owner Location of Reduction Method of Reduction
NOx
Elk Hills, Tupman, CA; Retrofit engines with pre-
S-2991-2 12/5/1990 9/25/2008 55,800 55,800 55,800 55,800 223,200 Pastoria Energy Facility, LLC STR NE35/30S/23E combustion chambers
SOx
Panama Ln & Weedpatch Hwy,
Bakersfield, CA 93307-9210 Reduction in refinery fuel gas
S-2726-5 10/4/2007 5/14/2008 55,614 40,150 0 84,936 180,700 Kern Oil & Refining Company STR 25/30S/28E H2S content prior to combustion
VOC
2365 E North Ave, Fresno, CA Shutdown of cotton gin (natural
C-348-1 10/2/1992 12/22/1999 10,250 10,250 10,250 10,250 41,000 Calpine Corporation 93725 gas-fired dryers)
Attachment 5.1F-1
Interpollutant Offset Analysis
ATTACHMENT 5.1F-1
Interpollutant Offset Analysis
The objective of an emission offset requirement is to ensure that new projects will have a net
air quality benefit in the region. The offset program seeks to achieve this by reducing
emissions at one location to balance, or offset, an emission increase elsewhere.
The simplest case involves the generation of emission offsets by reductions from an existing
source at, or near, the new source. When the pollutants are the same and the location is the
same, the presence or absence of a net air quality benefit is relatively easy to determine: if
the new emissions are less than the old emissions, a regional net air quality benefit is
achieved.
When the location of the source of offsets is different from the source of new emissions, the
areas impacted by the two sources differ. It is often impossible to demonstrate that the area
impacted by the new source is benefited everywhere by the reductions from the existing
source. Agencies usually address this by setting an offset ratio that takes distance into
account. The amount of reductions required is higher than the emission increase, resulting
in a net benefit to the region as a whole and to most locations in the impacted area as well.
This approach is usually coupled with a requirement to conduct an impact analysis to
ensure that no significant increases occur in those areas where the effect of the increase is
greater than the benefit from the decrease.
The analysis becomes much more complicated when the proposed reduction is of a different
pollutant than that emitted by the proposed new source. The principle is the same: a net air
quality benefit must be demonstrated. However, when the offsetting pollutant is different
than the new pollutant, the demonstration is not straightforward.
Although the statutory requirement is to show an overall net air quality benefit, the practice
has been to apply this test on a pollutant-specific basis. The agencies have allowed the
reduction of one pollutant to offset the increase of another pollutant only where the two
pollutants can be related, generally because one pollutant is a precursor for the other, or
both are precursors for a third pollutant.
The SJVAPCD is not in attainment with the state 24-hour standard for PM10. The District’s
new source review rule requires offsets for most increases in emissions of PM10 and its
precursors, which include NOx, SO2, VOC, and PM10. The A2PP project will be required to
provide offsets for all of these pollutants except SO2. TID has purchased NOx, SO2, VOC
offsets. However, the applicant has not been able to obtain sufficient PM10 offsets to offset
project PM10 with PM10 reductions.
SJVAPCD allows the use of interpollutant offsets, provided the project demonstrates a net
air quality benefit and the impact analysis demonstrates that the project does not worsen or
cause non-compliance with any ambient air quality standard.
The applicant proposes to meet the PM10 offset requirements for the A2PP by providing
interpollutant SO2 reductions. The direct impact analysis requirement, which demonstrated
EY012009003SAC(A2PP APPENDIX 5.1F_OFFSETS_REV-FINAL.DOC) 5.1F-7
APPENDIX 5.1F: OFFSETS AND INTERPOLLUTANT OFFSET RATIO ANALYSIS
that the PM10 emissions from the proposed project would not contribute significantly to an
existing violation, was addressed in Section 5.1.2.5. TID proposes to follow the District’s
March 2009 guidance (attached) and to provide SO2 reductions at a 1.0:1.0 ratio (not
including the distance ratio requirement in Rule 2201).
8 SAC/A2PP APPENDIX 5.1F_OFFSETS_REV-FINAL.DOC
APPENDIX 5.1F: OFFSETS AND INTERPOLLUTANT OFFSET RATIO ANALYSIS
Attachment 5.1F-1.1
SJVAPCD Interpollutant Offset Ratio
Explanation
EY012009003SAC(A2PP APPENDIX 5.1F_OFFSETS_REV-FINAL.DOC) 5.1F-9
Interpollutant Offset Ratio Explanation
The Air District’s Rule 2201, “New and Modified Source Review”, requires facilities to
supply “emissions offsets” when a permittee requests new or modified permits that allow
emissions of air contaminants above certain annual emission offset thresholds. In
addition, Rule 2201 allows interpollutant trading of offsets amongst criteria pollutants
and their precursors upon the appropriate scientific demonstration of an adequate
trading ratio, herein referred to as the interpollutant ratio. A technical analysis is
required to determine the interpollutant offset ratio that is justified by evaluation of
atmospheric chemistry. This evaluation has been conducted using the most recent
modeling analysis available for the San Joaquin Valley. The results of the analysis are
designed to be protective of health for the entire Valley for the entire year, by applying
the most stringent interpollutant ratio throughout the Valley.
It is appropriate for District particulate offset requirements to be achieved by either a
reduction of directly emitted particulate or by reduction of the gases, called particulate
precursors, which become particulates from chemical and physical processes in the
atmosphere. The District interpollutant offset relationship quantifies precursor gas
reductions sufficient to serve as a substitute for a required direct particulate emissions
reduction. Emission control measures that reduce gas precursor emissions at the
facility may be used to provide the offset reductions. Alternatively, emission credits for
precursor reductions may be used in accordance with District regulations.
The amount of particulate formed by the gaseous emissions must be evaluated to
determine how much credit should be given for the gaseous reductions. Gases
combine and merge with other material adding molecular weight when forming into
particles. Some of the gases do not become particulate matter and remain a gas. Both
the extent of conversion into particles and resulting weight of the particles are
considered to establish mass equivalency between direct particulate emissions and
particulate formed from gas precursors. The Interpollutant offset ratio is expressed as a
per-ton equivalency.
The District interpollutant analysis uses the most recent and comprehensive modeling of
San Joaquin Valley particulate formation from sulfur oxides (SOx) and nitrogen oxides
(NOx). Modeling compares industrial directly emitted particulate to particulate matter
from precursor emissions. The interpollutant modeling procedure, assumptions and
uncertainties are documented in an extensive analysis file. Additional documentation of
the modeling procedure for the San Joaquin Valley is contained in the 2008 PM2.5 Plan
and its appendices. The 2008 PM2.5 Plan provides evaluation of the atmospheric
relationships for direct particulate emissions and precursor gases when they are highest
during the fourth quarter of the year. The southern portion of the Valley is evaluated by
both receptor modeling and regional modeling of chemical relationships for precursor
particulate formation. Regional modeling was conducted for the entire Valley through
2014. The two modeling approaches are combined to determine interpollutant offset
ratios applicable to, and protective of, the entire Valley (SOx for PM 1:1 and NOx for PM
2.629:1).
APPENDIX 5.1F: OFFSETS AND INTERPOLLUTANT OFFSET RATIO ANALYSIS
Attachment 5.1F-1.2
SJVAPCD Development of the Interpollutant
Offset Ratio
EY012009003SAC(A2PP APPENDIX 5.1F_OFFSETS_REV-FINAL.DOC) 5.1F-13
DEVELOPMENT OF THE INTERPOLLUTANT RATIO
For the proposed substitution of reductions of sulfur oxides (SOx)
or nitrogen oxides (NOx) for directly emitted particulate matter
March 2009
INTRODUCTION .......................................................................................................................................................2
ANALYSES INCLUDED IN INTERPOLLUTANT EVALUATION ....................................................................3
FACTORS CONSIDERED ..............................................................................................................................................3
ELEMENTS FROM 2008 PM 2.5 PLAN .........................................................................................................................3
EXTENSION BY ADDITIONAL ANALYSIS ......................................................................................................................4
STRENGTHS ...............................................................................................................................................................4
LIMITATIONS .............................................................................................................................................................5
ANALYSES CONTAINED IN RECEPTOR MODELING.....................................................................................6
FACTORS CONSIDERED ..............................................................................................................................................6
ANALYSES IN RECEPTOR MODELING THAT USE INPUT FROM REGIONAL MODELING ...................................................6
EXTENSION BY ADDITIONAL ANALYSIS ......................................................................................................................6
STRENGTHS ...............................................................................................................................................................6
LIMITATIONS .............................................................................................................................................................7
ANALYSES CONTAINED IN REGIONAL MODELING .....................................................................................8
FACTORS CONSIDERED ..............................................................................................................................................8
EXTENSION BY ADDITIONAL ANALYSIS ......................................................................................................................8
STRENGTHS ...............................................................................................................................................................9
LIMITATIONS .............................................................................................................................................................9
RESULTS AND DOCUMENTATION....................................................................................................................10
DEVELOPMENT OF THE INTERPOLLUTANT RATIO
Introduction
Goal of Interpollutant Evaluation: Establish the atmospheric exchange
relationship for substitution of alternative pollutant or precursor reductions for
required reductions of directly emitted particulate
Evaluation to establish the atmospheric relationship of different pollutants is required as
a prerequisite for establishing procedures for allowing a required reduction to be met by
substitution of a reduction of a different pollutant or pollutant precursor. Proposed new
facility construction or facility modifications may result in increased emissions of a
pollutant. The District establishes requirements for reductions of the pollutant to “offset”
the proposed increase. A facility may propose a reduction of an alternative pollutant or
pollutant precursor where reductions of that material have already been achieved at the
facility beyond the amount required by District regulations or where emission reductions
credits for reductions achieved by other facilities are economically available; however,
for such a substitution to be allowed the District must establish equivalency standards
for the substitution. The equivalency relationship used for offset requirements is
referred to in this discussion as the interpollutant ratio. The interpollutant ratio is a
mathematical formula expressing the amount of alternative pollutant or precursor
reduction required to be substituted for the required regulatory reduction. This
discussion is limited to the atmospheric relationships and does not address other policy
or regulatory requirements for offsets such as are contained in District Rule 2201.
The following description is provided to explain key elements of the analysis conducted
to develop the atmospheric relationship between the commonly requested substitutions.
Emission reductions of sulfur oxide emissions or nitrogen oxide emissions are proposed
by many facilities as a substitution for reduction of directly emitted particulates.
Elemental and organic carbon emissions are the predominant case and dominant
contribution to directly emitted particulate mass from industrial facilities, although other
types of directly emitted particulates do occur. Therefore this atmospheric analysis
examines directly emitted carbon particulates from industrial sources in comparison to
the formation of particles from gaseous emissions of sulfur oxides and nitrogen oxides.
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DEVELOPMENT OF THE INTERPOLLUTANT RATIO
Analyses included in Interpollutant evaluation
Factors Considered
The foundation for this analysis is provided by the atmospheric modeling conducted for
the 2008 PM2.5 Plan. Modeling conducted for this State Implementation Plan was
conducted by the District and the California Air Resources Board using a variety of
modeling approaches. Each separate model has technical limitations and uncertainties.
To reduce the uncertainty of findings, a combined evaluation of results of all of the
modeling methods is used to establish “weight of evidence” support for technical
analysis and conclusions. The modeling methods are supported by a modeling protocol
which was sent to ARB and EPA Region IX for review and was included in the
appendices to the Plan.
The analysis file prepared for the interpollutant ratio evaluation includes emissions
inventories, regional model daily output files, chemical mass balance modeling and
speciated rollback modeling as produced for the 2008 PM2.5 Plan. This well examined
and documented modeling information was used as a starting point for additional
evaluation to determine interrelationships between directly emitted pollutants and
particulates from precursors.
The interpollutant ratio analysis is limited to evaluation of directly emitted PM2.5 from
industrial sources and formation of PM2.5 from precursor gases. While both directly
emitted particulates and particulate from precursor gases also occur in the PM10 size
range, there is much more uncertainty associated with deposition rates and particle
formation rates for the larger size ranges. Additionally, because PM2.5 is a subset of
PM10; all reductions of PM2.5 are fully creditable as reductions towards PM10
requirements. This analysis concentrates on the quarter of the year when both directly
emitted carbon from industrial sources and secondary particulates are measured at the
highest levels. Assessing atmospheric ratios at low concentrations is subject to much
greater uncertainty and has limited value toward assessment of actions to comply with
the air quality standards.
Elements from 2008 PM 2.5 Plan
• Regional modeling daily output for eleven locations
• Chemical Mass Balance (CMB) modeling for four locations – source analysis,
speciation profile selection, event meteorology evaluation
• Receptor speciated rollback modeling with adjustment for nitrate nonlinearity for four
locations, evaluation of spatial extent of contributing sources
• Emission inventories and projections to future years as developed for the 2008 PM
2.5 Plan
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DEVELOPMENT OF THE INTERPOLLUTANT RATIO
• Modeling protocols for receptor modeling, regional modeling, and Positive matrix
Factorization (PMF) analysis and evaluation of technical issues applicable to
particulate formation in the San Joaquin Valley
• Model performance analysis as documented in appendices to the 2008 PM 2.5 Plan
Extension by additional analysis
Additional evaluation was conducted to evaluate the receptor modeling relationship
between direct PM from industrial sources and sulfate and nitrate particulate formed
from SOx and NOx precursor gases. Area of influence adjustments were evaluated to
ensure appropriate consideration of contributing source area for different types of
pollutants for both directly emitted and secondary particulate. This evaluation was
possible only for the southern four Valley counties and was conducted for both 2000
and 2009.
The regional model output was evaluated for the fourth quarter to evaluate general
atmospheric chemistry in 2005 and 2014 to determine the correlation between northern
and southern areas of the Valley. This evaluation determined that the atmospheric
chemistry observed and modeled in the north was within the range of values observed
and modeled in the southern SJV. This establishes that a ratio protective of the
southern Valley will also be protective in the north.
The District determined from the additional analyses of both receptor and regional
modeling that the most stringent ratio determined for the southern portion of the Valley
would also be protective of the northern portion of the Valley. Due to the regional
nature of these pollutants, actions taken in other counties must be assumed to have at
least some influence on other counties; therefore to achieve attainment at the earliest
practical date it is appropriate to require all counties to establish a consistent
interpollutant ratio for the entire District.
Strengths
The interpollutant ratio analysis uses established and heavily reviewed modeling and
outputs as foundation data. Analysis of model performance has already been
completed for the models and for the emissions inventories used for this analysis. The
modeling was performed in accordance with protocols developed by the District and
ARB and in accordance with modeling guidelines established by EPA. The combination
of modeling approaches provides an analysis for the current year and provides
projection to 2014. Weight of evidence comparison of various modeling approaches
establishes the reliability of the foundation modeling, with all modeling approaches
showing strong agreement in predicted results. Additional analysis performed to
develop the interpollutant ratio uses both regional and receptor evaluations which were
the primary models used for the 2008 PM 2.5 Plan.
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DEVELOPMENT OF THE INTERPOLLUTANT RATIO
Limitations
Both industrial direct emissions and secondary formed particulate may be both PM2.5
and PM10. The majority of secondary particulates formed from precursor gases are in
the PM2.5 range as are most combustion emissions from industrial stacks, however
both secondary and stack emissions do contain particles larger than PM2.5. Regional
modeling is more reliable for the smaller fraction due to travel distances and deposition
rates. Large particles have much higher deposition and are much more difficult to
replicate with a regional model. This leads to a strong technical preference for
evaluating both emission types in terms of PM2.5 because the integration of receptor
analysis and regional modeling for coarse particle size range up to PM10 has a much
greater associated uncertainty.
5
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DEVELOPMENT OF THE INTERPOLLUTANT RATIO
Analyses contained in Receptor modeling
Factors Considered
This modeling approach uses speciated linear modeling based on chemical mass
balance evaluation of contributing sources with San Joaquin Valley specific
identification of contributing source profiles, adjustments from regional modeling for the
nonlinearity of nitrate formation, adjustments for area of influence impacts of
contributing sources developed from back trajectory analysis of high concentration
particulate episodes and projections of future emission inventories as developed for the
2008 PM2.5 Plan.
Analyses in receptor modeling that use input from regional
modeling
The receptor modeling analysis uses a modified projection of nitrate particulate
formation from nitrogen oxides based upon results of regional modeling. The
atmospheric chemistry associated with nitrate particulate formation has been
determined to be nonlinear; while the default procedures for speciated rollback
modeling assume a linear relationship. This adjustment has been demonstrated as
effective in producing reliable atmospheric projections for the prior PM10 Plans.
Extension by additional analysis
Additional evaluations were added to results of the receptor modeling performed for the
2008 PM2.5 Plan. Calculations determine the observed micrograms per ton of emission
for each contributing source category that can be resolved by chemical mass balance
modeling methods. These ten categories allow differentiation of industrial direct
emissions of organic and elemental carbon from other sources that emit elemental and
organic carbon. The interpollutant calculation is developed as an addition to the
receptor analysis by calculating the ratio of emissions per ton of directly emitted
industrial PM2.5 to the per ton ratio of secondary particulate formed from NOx and SOx
emissions. Summary tables and issue and documentation discussion was added to the
analysis.
Strengths
Receptor modeling provides the ability to separately project the effect of different key
sources contributing to carbon and organic carbon. This is critical for establishing the
atmospheric relationship between industrial emissions and the observed concentrations
due to industrial emissions. Regional modeling methods at this time do not support
differentiation of vegetative and motor vehicle carbon contribution from the emissions
form industrial sources. The area of influence of contributing sources was also
considered as a factor with the methods developed by the District to incorporate the
gridded footprint of contributing sources into the receptor analysis. While regional
6
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DEVELOPMENT OF THE INTERPOLLUTANT RATIO
models use gridded emissions, current regional modeling methods do not reveal the
resulting area of influence of contributing sources.
Limitations
Receptor modeling uses linear projections for future years and cannot account for
equilibrium limitations that would occur if a key reaction became limited by reduced
availability of a critical precursor due to emission reductions. The regional model was
used to investigate this concern and did not project any unexpected changes due to
precursor limitations.
7
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DEVELOPMENT OF THE INTERPOLLUTANT RATIO
Analyses contained in Regional modeling
Factors Considered
The analysis file includes the daily modeling output representing modeled values for the
base year 2005 and predicted values for 2014 for each of the eleven Valley sites that
have monitoring data for evaluation of the models performance in predicting observed
conditions. These sites are located in seven of the eight Valley counties. Madera
County does not have monitoring site data for this comparison.
Modeling data for all quarters of the year was provided. Due to the higher values that
occur due to stagnation events in the fourth quarter, both industrial carbon
concentrations and secondary particulates forming from gases are highest in the fourth
quarter. Evaluating the interpollutant ratio for other quarters would be less reliable and
of less significance to assisting in the reduction of high particulate concentrations.
Modeling for lower values has higher uncertainty. Modeling atmospheric ratios when
the air quality standard is being met are axiomatically not of value to determining offset
requirements intended to assist in achieving compliance with the air quality standard.
However, for consistency of analysis between sites, days when the standard was being
met during the fourth quarter were not excluded from the interpollutant ratio analysis.
Bakersfield fourth quarter modeled data included only eight days that were at or below
the standard. Fresno and Visalia sites averaged twelve days; northern sites 24 days
and the County of Kings 38 days.
Modeling output provided data for both 2005 and 2014. While there is substantial
emissions change projected for this period, the regional modeling evaluation does not
project much change in the atmospheric ratios of directly emitted pollutants and
secondary pollutants from precursor gases. This indicates that the equilibrium
processes are not expected to encounter dramatic change due to limitation of reactions
by scarcity of one of the reactants. This further justifies using the receptor evaluation
determining the interpollutant ratio for 2009 through the year 2014 without further
adjustment. If observed air quality data demonstrates a radical shift in chemistry or
components during the next few years, such a change could indicate that a limiting
reaction has been reached that was not projected by the model and such radical
changes might require reassessment of the conclusion that the ratio should remain
unchanged through 2014.
Extension by additional analysis
Regional modeling results prepared for the 2008 PM2.5 Plan were analyzed to extract
fourth quarter data for all sites. The atmospheric chemistry for all counties was
analyzed for consistency and variation. This analysis provided a determination that the
secondary formation chemistry and component sources contributing to concentrations
observed in the north fell within the range of values similarly determined for the
southern four counties. Based upon examination of the components and chemistry, the
northern counties would be expected to have an interpollutant ratio value less than the
8
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DEVELOPMENT OF THE INTERPOLLUTANT RATIO
ratio determined for Kern County but greater than the one for Tulare County. This
establishes that the interpollutant ratio determined by receptor analysis of the southern
four counties provides a value that is also sufficiently protective for the north.
Strengths
Regional models provide equilibrium based evaluations of particulate formed from
precursor gases and provide a regional assessment that covers the entire Valley. The
projection of particulate formed in future years is more reliable than linear methods used
for receptor modeling projections.
Limitations
The regional model does not provide an ability to focus on industrial organic carbon
emissions separate from other carbon sources such as motor vehicles, residential wood
smoke, cooking and vegetative burning. Regional modeling does not provide an
assessment method for determination of sources contributing at each site or the area of
influence of contributing emissions. Receptor analysis provides a more focused tool for
this aspect of the evaluation.
9
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DEVELOPMENT OF THE INTERPOLLUTANT RATIO
Results and Documentation
SJVAPCD Interpollutant Ratio Results
SOx for PM ratio: 1.000 ton of SOx per ton of PM
NOx for PM ratio: 2.629 tons of NOx per ton of PM
These ratios do not include adjustments for other regulatory
requirements specified in provisions of District Rule 2201.
The results of the modeling analysis developed an atmospheric interpollutant ratio for
NOx to PM of 2.629 tons of NOx per ton of PM. This result was the most stringent ratio
from the assessment industrial carbon emissions to secondary particulates at Kern
County; with Fresno, Tulare and Kings counties having a lower ratio. The assessment
of chemistry from the regional model required comparison of total carbon to secondary
particulates and is therefore not directly useful to establish a ratio. However, the
regional model does provide an ability to compare the general atmospheric similarity
and compare changes in chemistry due to Plan reductions. Evaluation revealed that the
atmospheric chemistry of San Joaquin, Stanislaus and Merced counties falls within the
range of urban characteristics evaluated for the southern four counties; therefore the
ratio established should be sufficiently protective of the northern four counties.
Additionally, comparison of future year chemistry showed minimal change in pollutant
ratio due to the projected changes in the emission inventory from implementation of the
Plan. The SOx ratio as modeled indicates a value of less than one to one due to the
increase in mass for conversion of SOx to a particulate by combination with other
atmospheric compounds; however, the District has set guidelines that require at least
one ton of an alternative pollutant for each required ton of reduction in accordance with
District Rule 2201 Section 4.13.3. Therefore the SOx interpollutant ratio is established
as 1.000 ton of SOx per ton of PM. These ratios do not include adjustments for other
regulatory considerations, such as other provisions of District Rule 2201.
A guide to the key technical topics and the reference material relevant to that topic is
found on the next page. References from the 2008 PM2.5 Plan may be obtained by
requesting a copy of that document and its appendices or by downloading the document
from http://www.valleyair.org/Air_Quality_Plans/AQ_Final_Adopted_PM25_2008.htm.
References in Italics are spreadsheets included in the interpollutant analysis file “09
Interpollutant Ratio Final 032909.xls” which includes 36 worksheets of receptor
modeling information from the 2008 PM2.5 Plan, 11 modified and additional
spreadsheets for this analysis and two spreadsheets of regional model daily output.
This file is generally formatted for printing with the exception of the two spreadsheets
containing the regional model output “Model-Daily Annual” and “Model-Daily Q4” which
are over 300 pages of raw unformatted model output files. The remainder of the file is
formatted to print at approximately 100 pages. This file will be made available on
request but is not currently posted for download.
10
IP Ratio Development (3).doc
DEVELOPMENT OF THE INTERPOLLUTANT RATIO
Interpollutant Ratio Issues & Documentation
TOPIC Reference
1 Reason for using PM2.5 for establishing the substitution relationship
between direct emitted carbon PM and secondary nitrate and sulfate 2008 PM2.5 Plan,
PM: consistency of relationship between secondary particulates and Sections 3.3.2
industrial direct carbon combustion emissions. through 3.4.2
2 Reason for using 4th Quarter analysis: Highest PM2.5 for all sites. DV Qtrs
3 Reason for using analysis of southern SJV sites to apply to regional Q4 Model Pivot,
interpollutant ratio: Northern site chemistry ratios are within the range of Model-site chem,
southern SJV ratios. Peak ratio will be protective for all SJV counties. Model-Daily Q4
4 Reason for using combined results of receptor and regional model:
Receptor model provides breakdown of different carbon sources to isolate 2008 PM2.5 Plan,
connection between industrial emissions and secondary PM. Appendix F
Regional model provides atmospheric information concerning the northern 2008 PM2.5 Plan,
SJV not available from receptor analysis. Appendix G
5 Most significant contributions of receptor evaluation: Separation of
industrial emissions from other source types. Area of influence evaluation for 2008 PM2.5 Plan,
contributing sources. Appendix F
6 Most significant contributions of regional model: Scientific equilibrium
methods for atmospheric chemistry projections for 2014. Receptor technique 2008 PM2.5 Plan,
is limited to linear methods. Appendix G
7 Common area of influence adjustments used for all receptor
evaluations:
Geologic & Construction, Tire and Brake Wear, Vegetative Burning -
Modeling
contribution extends from more than just the urban area (L2)
evaluation by
Mobile exhaust (primary), Organic Carbon (Industrial) primary, Unassigned - J. W. Sweet
contribution extends from more than larger area, subregional (L3) February 2009
Secondary particulates from carbon sources are dominated by the local area Reflected in IPR
with some contribution from the surrounding area (average of L1 and L2) County 2000-2009
Marine emissions not found present in CMB modeling for this analysis. worksheets
8 Variations to reflect secondary area of influence specific to location:
Fresno: Evaluation shows extremely strong urban signature (L1) for Modeling
secondary sources evaluation by
Kern: Evaluation shows a strong urban signature mixed with emissions from J. W. Sweet
the surrounding industrial areas (average L1 and L2) for both carbon and February 2009
secondary sources Reflected in IPR
Kings and Tulare: Prior evaluation has show a shared metropolitan County 2000-2009
contribution area (L2) worksheets
9 Reasons for using 2009 Interpollutant Ratio Projection:
2009 Interpollutant ratio is consistent with current emissions inventories 2008 PM2.5 Plan
Regional modeling does not show a significant change in chemical
Q4 Model Pivot
relationships through 2014.
10 Reason for using SOx Interpollutant Ratio at 1.000: A minimum offset District Rule 2201
ratio is established as 1.000 to 1.000 consistent with prior District policy and Section 4.13.3
procedure for interpollutant offsets.
11
IP Ratio Development (3).doc
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